Heretofore, there has been known an electromotive spot welding gun which allows a movable electrode tip to advance to and retreat from a fixed electrode tip. For example, in Patent Document 1, there is disclosed a welding gun which allows a rod including a movable electrode tip at a front edge thereof and inserted into a hollow rotor of a motor to advance to and retreat from a gun main body by a rotating movement of a feed screw mechanism coupled to the hollow motor.
Meanwhile, to prevent failure of the welding gun at the failure of a controller of the welding gun, the input of a wrong set value into the controller by an operator, or the like, there is required a stopper mechanism which regulates an advancing/retreating movement of the rod out of a stipulated region.
For example, when the rod projects out of the stipulated region and drops down from the gun main body, the welding gun cannot be restored. Therefore, to regulate the projecting of the rod, a flange section is formed at an upper end of the rod, and a stopper ring is disposed in a hollow housing of the motor. In consequence, when the rod projects out of the stipulated region, the flange section abuts on the stopper ring to prevent the rod from protruding.
Moreover, when the rod retracts out of the stipulated region to collide with the bottom surface of the hollow rotor of the motor, the feed screw mechanism fails. Therefore, to regulate the retraction of the rod, stoppers are arranged at an upper end of the gun main body and an upper end of a fixing portion of the movable electrode tip fixed to the rod, respectively. In consequence, when the rod retracts out of the stipulated region, these stoppers abut, whereby the further retraction movement of the rod is prevented.